A standard top brand OEM DVD rewriter optical drive, which will read and write to both CD and DVD media, is less than £20.
All that needs to be done is to turn the system off but still connected to the mains (to maintain an earth), take out the screws on each side of the case (keep them for the new drive if necessary), note the power lead and IDE cable positions before disconnecting, pull the drive out of the front of the case and replace it with the new one.
Reconnect the power lead and IDE cable, making sure they are firmly attached; replace the case parts and turn the power on to the system again.
When you Reboot, Windows will Find New Hardware and reinstall the basic CDROM driver, which is all that is required.
The burning duties of a rewriter are undertaken using software such as Nero.